Self-lubricated coating and method

ABSTRACT

Coating and method for providing a self-lubricated coating on a substrate. The method includes spraying with an inert gas at least a layer of liquid metal on the substrate; adding a compound to the liquid metal while being sprayed on the substrate; forming a porous layer on the substrate that includes the metal and the compound, where the porous layer has plural pores; heating the porous layer to open the pores; flooding the open pores with a greasing substance such that part of the greasing substance is stored in one or more pores; and cooling the porous layer to close the pores and trap the greasing substance inside the pores.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a national stage application under 35 U.S.C. §371(c) of prior-filed, co-pending PCT patent application serial number PCT/EP2011/055123, filed on Apr. 1, 2011, which claims priority to Italian Patent Application Serial No. CO2010A000014, filed on Apr. 6, 2010, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Embodiments of the present invention relate generally to methods and systems and, more particularly, to mechanisms and techniques for providing a self-lubricated coating.

During the past years, with the increase in price of fossil fuels, the interest in various aspects related to the processing of the fossil fuels has increased. In addition, there is an increased interest in producing more efficient and reliable motors, turbines, compressors, etc. to facilitate a better production and distribution of oil and gas based products.

Such machines generally include a fixed part, the stator, and a rotating part, the rotor. The rotor is configured to rotate relative to the stator to achieve one of compressing a medium, producing electrical energy, or transforming electrical energy into mechanical energy. The rotor needs to rotate relative to the stator with minimum friction and in a certain temperature range. Because of the continuous rotation of the rotor and its weight (which might be between 20 and 20,000 kg and increases the friction), a large amount of heat is produced. The heat appears mainly in the bearings that support the rotor.

Thus, various mechanisms for cooling the bearings may be used. One such mechanism is to continuously circulate a medium, oil for example, between the rotor and the bearings and to remove the excessive heat by cooling the oil. A pump may be used to force the circulation of the oil. However, if the pump fails, the oil stops flowing and consequently, stops removing the heat developed at an interface between the rotor and the bearing. Under these circumstances, no oil may be present at the interface between the rotor and the bearing, which determines an increase of the temperature of the bearing up to a point that will result in damages to the rotor and/or the bearing or other component of the machine.

If this abnormal condition is not rapidly identified by the operator of the machine or by a dedicated system so that the machine is stopped, the entire machine may be severely damaged, resulting in the interruption of the whole process in which the machine is involved, which is costly and undesirable in the oil and gas industry. Even if the failed condition of the machine is quickly identified, sometimes it may be impossible to immediately stop the affected machine as the machine is part of a process in which multiple machines are coordinated and the quick shut down of one machine is not possible without interfering with the safety of the other machines.

Accordingly, it would be desirable to provide systems and methods that offer the operator of the machine a time buffer between the instant when the machine has failed to work properly and the instant when the machine is damaged due, for example, to the high temperature that appears when the oil pump fails.

BRIEF DESCRIPTION OF THE INVENTION

According to one exemplary embodiment, there is a method for providing a self-lubricated coating on a substrate. The method includes spraying with an inert gas at least a layer of liquid metal on the substrate; adding a compound to the liquid metal while being sprayed on the substrate; forming a porous layer on the substrate that includes the metal and the compound, where the porous layer has plural pores; heating the porous layer to open the pores; flooding the open pores with a greasing substance such that part of the greasing substance is stored in one or more pores; and cooling the porous layer to close the pores and trap the greasing substance inside the pores.

According to still another exemplary embodiment, there is a method for operating a turbo-machinery having a safety mechanism for a bearing. The method includes rotating a rotor relative to a stator of the turbo-machinery; supporting the rotor with a bearing that includes at least a porous layer, the at least a porous layer including a metal and a compound that form plural pores and a greasing substance stored in the pores; and providing a lubricant to the bearing while the rotor rotates such that an operation temperature of the bearing is substantially constant.

According to yet another exemplary embodiment, there is a turbo-machinery that includes a stator configured to be fix; a rotor configured to rotate relative to the stator; a bearing configured to support the rotor and facilitate a rotation of the rotor; and a self-lubricated coating provided on the bearing or the rotor. The self-lubricated coating includes at least a porous layer, the at least a porous layer including a metal and a compound that form plural pores and a greasing substance stored in the pores, and the pores are closed trapping the greasing substance when an operational temperature of the bearing is below a predetermined value.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:

FIG. 1 is a schematic diagram of a machine having a rotor and a stator;

FIG. 2 is a schematic diagram of a substrate having a self-lubricated coating according to an exemplary embodiment;

FIG. 3 is an illustration of a porous layer according to an exemplary embodiment;

FIG. 4 is a flow chart illustrating a method for providing a self-lubricated coating on a substrate according to an exemplary embodiment; and

FIG. 5 is a flow chart illustrating a method for operating a turbo-machinery having a safety mechanism for a bearing according to an exemplary embodiment.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS OF THE INVENTION

The following description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to the terminology and structure of a compressor. However, the embodiments to be discussed next are not limited to compressors, but may be applied to other systems that include a rotor supported by bearings.

Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

According with an exemplary embodiment, part of the rotor, the bearing or both of them are coated with a self-lubricated coating that is configured to store a greasing material while the machine operates at a normal temperature and to release the greasing material when the temperature of the machine increases over a certain threshold temperature.

According to an exemplary embodiment shown in FIG. 1, a compressor 10 includes, among other things, a rotor 12 that is configured to rotate relative to a rotor 14. The rotor 12 is supported, for example, at both ends, by one or more bearings 16. Various bearings are known in the art and any of these bearings may be used to support the rotor 12. One example of a bearing is a journal bearing, which is described in U.S. Pat. No. 6,361,215, the entire content of which is incorporated herein by reference.

A journal bearing 16 uses one or more pads 18 that support the rotor 12 and oil is injected between the pads 18 and the rotor 12 at an interface 20 to reduce friction and/or to cool the interface. A pump (not shown) may be used to pump the oil through a channel 22 in each pad at the interface 20 between the pad 18 and the rotor 12. If the oil fails to be delivered at the interface 20, the temperature at this interface would increase beyond an acceptable value, which may damage the bearing 16, the rotor 12 or both of them.

According to an exemplary embodiment shown in FIG. 2, a portion of either the rotor 12, or the bearing 16, or both of them may be coated with a self-lubricated layer 24. The self-lubricated layer 24 may be deposited, as shown in FIG. 2, on a substrate 26, which may be one of the rotor 12 and/or the bearing 16. When the self-lubricated layer 24 is deposited on the rotor 12, it is desired that this layer be deposited to directly face the bearing 16.

Layer 24 may include a base material 28 that is deposited on the substrate 24. The base material may include a metal used for the bearing, e.g., gray cast iron, stainless steel, carbon steel, non-ferrous alloys, etc. In one application, the base material is plastic, e.g., includes a material with a low carbon content and high content of Fe, Ni or Cobalt. In another application, the base material does not includes Cr. In still another application, the base material may include a non-ferrous metal so that the base material is plastic. The base material may be deposited by methods known in the art. For example, the base material may be sprayed on the substrate. However, in one application the base material layer 28 is not part of the layer 24. Base material layer 28 is deposited to ensure a better adherence between the self-lubricated layer 24 and the substrate 26.

A porous layer 30 that provides the self-lubricated functionality is formed on the base material layer 28 or directly on the substrate 26. Porous layer 30 may include a metal and a compound that promotes the formation of pores in the porous layer 30. The metal may be one or more of a metal used for the bearing, e.g., gray cast iron, stainless steel, carbon steel, etc., depending on the application, the desired hardness of the layer, the load of the bearings. The compound may be one or more of graphite powder, Molybdenum disulfide (MoS₂), Tungsten sulfide (WS₂). The metal is sprayed as a liquid on the base material layer 28. For example, electric arc or plasma spray may be used for spraying the liquid metal and compound. An inert gas under pressure may be used to not only deliver the melted metal from the gun or other device used for coating the substrate but also to insert the compound into the melted metal. For example, the inert gas may be nitrogen (N).

Porous layer 30 is shown in FIG. 3 to have plural pores 32 distributed through the metal and compound mixture 34. The number of the plural pores 32 depends on many variables. For example, the number of pores may depend on the temperature at which the liquid metal is sprayed on the substrate, the pressure of the inert gas, the distance between the gun that sprays the liquid metal and the substrate, the specific metal used, the specific compound used, etc. In one application, the thickness of the self-lubricated layer 30 is between micrometers and millimeters.

Once the porous layer 30 has been formed on the substrate 26 and the temperature of the assembly is lowered around room temperature (e.g., 25° C.), the pores are closed, e.g., if the porous layer 30 is immersed in a bath of liquid, an insignificant amount of that liquid enters the pores of layer 30. However, if the layer 30 together with the substrate 26 are exposed (e.g., immersed) into an oil bath at a high temperature, the pores 32 of layer 30 open up and the oil starts flooding the pores. The high temperate range may be from 80 to 500° C., depending for example, on the type of oil (synthetic or not, etc.). The oil is used as an example but any greasing material may be used to partially fill part or all of the pores of the layer 30.

The substrate 26 and layer 30 are then cooled down to the room temperature to seal the pores such that the absorbed greasing material is stored inside the pores 32. Such substrate having the self-lubricated layer 30 is then used in one or more of the machines discussed above. Thus, when such a machine fails to provide oil at an interface between the rotor and the bearing, the temperature at the interface increases past the temperature for opening the pores of the self-lubricated layer 30, which determines the porous layer 30 to start releasing the greasing material at the interface between the rotor and the bearing.

Such a self-lubricated layer 30, depending on its size and distribution on the bearing and/or rotor, may provide the operator of the machine with minutes if not hours of safe operation although the main oil supply mechanism of the machine has failed. In this way, the operator has the necessary time to shut down the entire processing line in a controlled manner without impairing the safety of the other machines making up the processing line.

While it may be intuitive to provide a thick self-lubricated layer 30 in order to provide a longer supply of the greasing material, it has been found that a thick layer is prone to cracks, and thus, a shorter life. Further, the cracks in the thick layer allow the greasing material to escape earlier than desired and also may compromise the adherence of the porous layer to the substrate. On the contrary, a thin layer is not desirable as not enough greasing material may be stored. Thus, an appropriate thickness of the self-lubricated layer 30 depends on the type of machine, the weight of the rotor, the number of pads and the number of bearings, etc.

According to an exemplary embodiment illustrated in FIG. 4, there is a method for providing a self-lubricated coating on a substrate. The method includes a step 400 of spraying with a gas at least a layer of liquid metal on the substrate; a step 402 of adding a compound to the liquid metal while being sprayed on the substrate; a step 404 of forming a porous layer on the substrate that includes the metal and the compound, where the porous layer has plural pores; a step 406 of heating the porous layer to open the pores; a step 408 of flooding the open pores with a greasing substance such that part of the greasing substance is stored in one or more pores; and a step 410 of cooling the porous layer to close the pores and trap the greasing substance inside the pores.

It is noted that the gas used to deposit the liquid metal may be an inert gas. However, for depositing ferrous layers, a N₂ gas may be used as N₂ is cheaper. Also, the N₂ gas may provide more plasticity to the porous layer, which is desirable. The N₂ gas is better than the Argon or compressed air as this gas avoids oxidation of alloying elements in the liquid metal and also does not alter the composition of the deposited layer.

According to an exemplary embodiment shown in FIG. 5, there is a method for providing a safety mechanism for a bearing in a turbo-machinery. The method includes a step 500 of rotating a rotor relative to a stator of the turbo-machinery; a step 502 of supporting the rotor with a bearing that includes at least a porous layer, the at least a porous layer including a metal and a compound that form plural pores and a greasing substance stored in the pores; and a step 504 of providing a lubricant to the bearing while the rotor rotates such that an operation temperature of the bearing is substantially constant.

The disclosed exemplary embodiments provide a system and a method for providing a greasing material when a dedicated supply of the greasing material fails. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.

Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.

This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims. 

What is claimed is:
 1. A method for providing a self-lubricated coating on a substrate, the method comprising: spraying with a gas at least a layer of liquid metal on the substrate; adding a compound to the liquid metal while being sprayed on the substrate; forming a porous layer on the substrate that includes the metal and the compound, wherein the porous layer has plural pores; heating the porous layer to open the pores; flooding the open pores with a greasing substance such that part of the greasing substance is stored in one or more pores; and cooling the porous layer to close the pores and trap the greasing substance inside the pores.
 2. The method of claim 1, wherein the liquid metal is one of a metal used for a bearing, gray cast iron, stainless steel, carbon steel, or non-ferrous alloys.
 3. The method of claim 1, wherein the compound is one of graphite powder, Molybdenum disulfide (MoS₂), Tungsten sulfide (WS₂), or a combination thereof.
 4. The method of claim 1, further comprising: providing a base material that includes a low carbon content and high content of Fe, Ni or Cobalt or a plastic non-ferrous metal on the substrate prior to spraying so that the porous layer is formed on the base material to better adhere to the substrate.
 5. The method of claim 1, wherein the heating is achieved by immersing the porous material in the greasing substance at a predetermined temperature.
 6. The method of claim 1, wherein the substrate is a bearing of a compressor.
 7. The method of claim 1, wherein the gas includes nitrogen (N).
 8. A method for operating a turbo-machinery having a safety mechanism for a bearing, the method comprising: rotating a shaft relative to a stator of the turbo-machinery; supporting the shaft with a bearing that includes at least a porous layer, the at least a porous layer including a metal and a compound that form plural pores and a greasing substance stored in the pores; and providing a lubricant to the bearing while the shaft rotates such that an operation temperature of the bearing is substantially constant.
 9. The method of claim 8, further comprising: failing to provide the lubricant; increasing an operation temperature of the bearing; and opening the pores of the at least a porous layer such that the stored greasing substance exits the pores and lubes the bearing.
 10. A turbo-machinery, comprising: a stator configured to be fix; a shaft configured to rotate relative to the stator; a bearing configured to support the shaft and facilitate a rotation of the shaft; and a self-lubricated coating provided on the bearing or the shaft, wherein the self-lubricated coating includes at least a porous layer, the at least a porous layer including a metal and a compound that form plural pores and a greasing substance stored in the pores, and wherein the pores are closed trapping the greasing substance when an operational temperature of the bearing is below a predetermined value. 